Electric furnace for ceramics



Nov. 21, 1967 R. BUCHKREMER 3,354,293

ELECTRIC FURNACE FOR CERAMICS Filed June 9, 1965 2 Sheets$hee t 1 Fig.1

In ver) (or:

RUDOLF BUCHKREMER BY ATTORNEY.

Nov. 21, 1967 R. BUCHKREMER ELECTRIC FURNACE FOR CERAMICS 2 Sheets-Sheet 2 Filed June 9, 1965 t E M.

In van for RUDOLF BUCHKREMER BY alum! ATTORNEY.

United States Patent 3,354,293 ELECTRIC FURNACE FOR CERAMICS Rudolf Buchkremer, Numberg, Germany, assignor to Ludwig Riedhammer G-m.b.H., Nurnberg, Germany Filed June 19,, 1965, Ser. No. 462,663 Claims Priority, application Germany,

June 16 1964, R 38,137

3 Claims. (Cl. 219-388) ABSTRACT OF THE DISCLOSURE A furnace for advancing objects step-by-step along a furnace tunnel including a rocker-bar structure, the rockerbars being directed longitudinally of the tunnel and comprising alternative movable and fixed bars wherein the movable bars are connected together and supported on pillars fixed to two frame members which repeatedly perform an up-forward-down-and-back oscillatory movement, with the furnace also including electrical heating elements disposed above and below the rocker-bars.

This invention concerns rocker bar ovens or furnaces, that is to say ovens or furnaces constructed with a support, for articles passing through the oven or furnace, in the form of a rocker bar conveyor.

Such rocker bar conveyors have been known for some years in the steel industry, and are finding favour in the ceramics industry, in furnaces and ovens wherein articles to. be subjected to heat treatment are fed in continuous succession through the furnace or oven, which is generally of tunnel-like construction. Usually, they consist of a plurality of longitudinal bars lying side-by-side and extending longitudinally in the feed direction through the furnace, a drive arrangement being provided for raising a group of the bars, shifting them longitudinally in the feed direction, lowering them, and then returning them to their starting position, so that articles in the furnace and supported by the conveyor are raised off the other bars, forwards a short distance, and then deposited on such other bars whilst the group returns to its starting position.

In this way, the articles are progressed stepwise through the oven or furnace, and it will be evident that the bars can, for example, be divided into two groups one of which is provided with the drive arrangement just described and the other of which is fixed or stationary. Alternatively, each of the groups can be provided with its respective drive arrangement, these beingrelated to one another so that the one group is being lowered at the end of its movement in the feed direction whilst the other group is being raised in its starting position, so that the actual progression' of the articles is effected by both groups of bars in turn.

In the-rocker bar furnace or oven constructions already known, the movable bars are individually supported by a common base, which is disposed beneath the floor of the furnace and is adapted to perform movements corresponding to the desired bar movements, by way of individual respective supports which extend vertically downwards through appropriate elongate apertures in the floor of the furnace or oven. Usually, each bar is not a continuous bar but is formed by a plurality of separate bar sections arranged end-to-end in the feed direction through the furnace, and as a consequence the prior constructions involve a large number of rows of elongate apertures, each row of apertures extending transversely relative to the feed direction, and the rows being spaced apart at short intervals in the feed direction.

Because of these apertures, which are considerable in number, there are substantial heat losses from the furnace or oven, and the thermal inertia is very high, the latter factor being influenced by the fact that the bars have, hitherto, generally been constructed of brickwork. Moreover, the apertures have made it very difficult to equip the floor of the furnace or oven with electrical heating arrangements.

An object of this invention is to provide a rocker bar furnace or oven construction as aforesaid but wherein the above-discussed difiiculties are minimised, so that the furnace will have low heat losses and low thermal inertia, and can readily be equipped with electrical heating both for floor and ceiling, so that it is particularly suitable for use in the ceramic industry, for the high speed firing or baking of ceramic articles such as floor tiles, wall tiles, ceramic slabs, and the like.

With this object in view, the present invention provi-des a rocker bar furnace or oven comprising a rocker bar conveyor including bars extending longitudinally in the feed direction through the furnace or oven, a group of said bars being adapted to be raised, shifted in the feed direction, lowered and then returned to their starting position so as to progress articles stepwise through the furnace or oven, wherein the ends of said groups of bars are supported upon respective cross members which extend transversely to the feed direction and are adapted to be driven to raise, shift, lower and return said group of bars.

The bars may, of course, each be composed of a plurality of bar sections arranged end to end in the feed direction, and each bar or bar section of the group is preferably supported upon its respective cross member by way of support legs which clear corresponding cross members supporting the remaining bars or bar sections, and vice versa In a preferred embodiment of the invention, the cross members of the aforesaid group of bars are supported by their ends by uprights extending through elongate apertures in the floor of the furnace or oven, driving means being provided beneath said floor for displacing the uprights and thereby to transmit the necessary raising, shifting, lowering and returning movements to the cross members of said group.

With such preferred embodiment of the invention, the large number of elongate apertures previously necessary for the respective bars is rendered unnecessary, and only a small number of apertures is needed, these being at comparatively widely spaced intervals along the floor of the furnace or oven adjacent each lateral edge thereof. Accordingly, heat losses are reduced, and the floor of the furnace is comparatively free for the installation of electrical heating elements.

The uprights may conveniently be in the form of tubes, and these, as Well as the bars, the legs thereof and the cross members are advantageously of a ceramic materiial. If the furnace or oven is to be employed at comparatively low temperatures, such parts can alternatively be of steel having good high-temperature characteristics. This is particularly advantageous in conjunction with electrical heating both from below and above the bars, since fiat articles, such as floor tiles and the like, being progressed through the furnace or oven, are heated all around and consequently need to be subjected to firing for a fraction of the period hitherto necessary. For example, with previous furnace constructions several hours were necessary for the finish firing of a tile whereas this period is cut to less than thirty minutes with the construction of the invention.

To prevent articles being progressed by the conveyor from moving olf course, (i.c. from moving in a direction including a component which is transverse to the feed direction) upwardly projecting ridges are conveniently provided on two of the bars of the rocker bar conveyor. Such ridges are conveniently provided at a spacing, transversely of the feed direction, equal to the corresponding dimension of the articles.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic fragmentary end elevation of a rocker bar furnace constructed in accordance with the present invention;

FIG. 2' is a cross-sectional end elevation through the furnace of FIG. 1;

!FIG. 3 is a cross-sectional side elevation corresponding to the line III-III of FIG. 2;

FIG. 4 is a detached diagrammatic fragmentary perspective view showing certain of the parts of the furnace of FIGS. 1 to 3; and

FIG. 5 is a diagrammatic perspective view of one bar section of the furnace of FIGS. 1 to 4.

The furnace illustrated comprises a tunnel-like structure 1 (FIG. 1) of brickwork, fireclay, or other heat resistant material, providing a floor 8 above which'is disposed a rocker bar conveyor (indicated generally by reference numeral 2 in FIG. 2) which serves to progress articles to be subjected to heat treatment (not shown) stepwise through the furnace. I

The rocker bar conveyor 2 comprises a plurality of bars 3 and 4 extending longitudinally in the feed direction through the furnace and being disposed parallel to one another. The bars 3 and 4 alternate with one another as can be seen from FIG. 2, the bars 3 being fixed or stationary and the bars 4 being displaceable in unison as a group in a manner which will later be described in detail.

FIG. 4 shows some of the bars 3 and 4 with the spacing therebetween substantially exaggerated, and FIG. 5 shows one section of one of the bars, both the bars 3 and 4'being formed of a plurality of such sections arranged end to end longitudinally of the feed direction. In the case of the fixed bars 3, each bar section comprises a linear top portion 7 having an integral downwardly projecting foot 5 at each end thereof, whilst the sections of the displaceable bars 4 each comprise a linear top portion with integral downwardly projecting feet 5, so that each such section is generally of the form of an inverted-U, the limbs being comparatively short.

In the case of the sections of the fixed bars 3, stationary cross members 6 extend transversely of the feed direction, such cross members 6 being supported by the floor structure 8 of the furnace, and the feet 5 of such fixed bar sectionsrest upon and are supported by corresponding ones of such cross members 6.

In the case of the sections of the displaceable bars 4, a displaceable cross member 9 is arranged adjacent each stationary cross member 6, and such displaceable cross members 9 are each supported, at each end, by respective uprights or pillars 11 which extend downwards through elongate apertures or openings 15 provided in the floor structure 8 of the furnace. At their lower ends, the uprights 11 are connected to one or other of two longitudinal frame members 12 constituting part of drive means for displacing the displaceable cross members 9 in a manner whichwill later be described. The displaceable bar sections are supported, by way of their feet 5, upon respective ones of the cross members 9.

' The pillars or uprights 11 are advantageously of tubular form, andthese, together with the cross members 6 and 9 and the bar sections with the feet 5 formed integrally therewith, are all conveniently made of ceramic material,

although in the case of a furnace or oven intended to be run at comparatively low temperatures these parts may be of steel having good high-temperature characteristics.

As will be seen from FIGS. 1 and 2, the two outermost bars are formed with longitudinally extending upwardly projecting ridges 16. These ridges serve, in operation of the rocker bar conveyor 2, to confine articles moving along the conveyor to the feed direction which is longiof the articles being displaced in such manner as to in- I clude a component of movement transverse to the feed direction. In the illustrated case, the outermost bars are, in fact, displaceable bars 4, but it will be appreciated that such ridges 16 would be equally effective if the outermost bars were stationary bars and the ridges were provided thereon. If desired, the ridges 16 can be provided upon bars other than the outermost bars, provided the transverse spacing of the ridges 16 is substantially equal to or just greater than the corresponding dimensions of the articles to be conveyed through the furnace. The ridges 16 are, of course, formed integrally with the respective bar sections.

Disposed above the bars of the rocker bar conveyor and set, by their ends, into the opposite side walls of the tunnel structure so as to be spaced somewhat downwards from the roof of the structure are electrical heating elements 17, these each extending transversely to the feed direction. Similar electrical heating elements 18, also extending transversely to the feed direction, are set into respective recesses in the fi-oor structure 8 of the furnace, so as to be disposed below the bars of the rocker bar conveyor 2. The heating elements 17 and 18 are adapted for independent adjustment as to wattage and temperature.

Operation of the furnace is as follows. Assuming that a succession of articles (not shown) such as ceramic tiles, is being supplied to the conveyor 2, and the heating elements 17 and 18 are energised to heat the furnace, the conveyor 2 serves to progress the articles in a substantially endless succession through the furnace, for firing or heat treating them, in a series of successive small steps, all the articles being forwarded in the feed direction by a small step and then permitted to dwell for a very short period before the next step forward. This is achieved by the driving mechanism, including the frame members 12 firstly raising all of the uprights 11, and with them the cross members 9 and the movable bars 4, by a small distance in the direction indicated by the arrow A in FIG. 2. This lifts the articles so as just to be clear of the fixed bars 3. The driving mechanism then shifts its frame members 12 in the feed direction, as indicated by the arrow B of FIG. 3, by a short distance, so that the movable bars 4 are correspondingly moved, the apertures or openings 15 in the floor 8 of the furnace permitting the uprights 11 to move in the feed direction. Thereupon, the movable bars 4 are lowered so that the articles come to rest on the fixed bars 3, such movable bars 4 being lowered, as indicated by the arrow C in FIG. 2, so as just to disengage from the articles which'accordingly are deposited upon the fixed bars at a forwardly displaced position as compared with the starting position. The movable bars 4, whilst still lowered, are now returned to their initial positions by movement in the direction opposed to the arrow B, whereupon the cycle just described is repeated, each such cycle serving to move the articles a step forward through the furnace.

It will be appreciated from the foregoing that the multitudinous elongate apertures necessary in the floors of the prior known rocker bar furnaces to accommodate the movable bars are obviated and that the furnace floor is comparatively free of obstructions and apertures so that there is comparatively little heat loss and the heating elements 18 can be embodied into the furnace below the bars of the conveyor very simply and without much trouble. v v

The invention is not confined to the precise details of the foregoing example and variations may be made thereto, if desired. A most important point lies in the fact that the invention is not confined to the case wherein there is a single group of'di's-placeable bars and the remaining bars are fixed" as in the described embodiment. Thus, the bars 3 could, if desired, be provided as a, second displaceable ,groupof bars havingits .own driving mechanism, the arrangement being such that when the one group of bars is forwarding the articles the other is returning to its initial position and vice versa, so that the two groups serve in turn to forward the articles in the feed direction. The bars 3 and 4 could, of course be continuous bars throughout the length of the furnace if necessary being supported at appropriate intervals by respective feet 5 and cross members 6 or 9.

I claim:

1. An electrically-heated furnace for ceramics and walking beam conveyor therefor comprising the combination:

(a) a tunnel structure;

(b) means for heating the interior of said tunnel structure;

(c) a first set of spaced cross-members of ceramic material disposed within said tunnel structure transversely of the line of conveying movement therethrough;

(d) first carrier members each of ceramic material and of generally U-sha-pe supported at their opposite ends on adjacent cross-members of said first set in end-toend relationships for defining a first group of spaced longitudinally-disposed carriers;

(e) a second set of spaced cross-members of ceramic material disposed within said tunnel structure transversely of the line of conveying movement therethrough and arranged in alternating disposition with respect to the cross-members of said first set;

(f) second carrier members each of ceramic material and of generally U-shape supported at their opposite ends on adjacent cross-members of said second set in end-to-end relationships for defining a second group of spaced longitudinally disposed carriers arranged in alternating disposition with respect to the carriers of said first group; (g) means for displacing the cross members of said 5 second set and the second carrier members relative to the cross members of said first set upwardly and forwardly in feeding direction and downwardly and rearwardly in non-feeding direction. 2. A furnace structure according to claim 1, further 10 including:

(h) upper electric heating elements mounted above said first and second carrier members;

(i) lower electric heating elements mounted below said first and second carrier members, said upper and lower electric heating elements being separately adjustable.

3. A furnace according to claim 2 wherein upwardly projecting guide ribs are provided on carrier members forming carriers spaced by the width of an article being fired.

References Cited UNITED STATES PATENTS 1,638,937 8/1927 Keene 263-6 X 1,741,516 12/1929 Hansen 198219 1,883,763 10/1932 Cochran 198-219 1,897,911 2/1933 McCann et al. 263-6 1,909,906 5/1933 Smallwood et al. 198-219 1,920,133 7/1933 Summey 263-6 RICHARD M. WOOD, Primary Examiner. C. L. ALBRITTON, Assistant Examiner. 

1. AN ELECTRICALLY-HEATED FURNACE FOR CERAMICS AND WALKING BEAM CONVEYOR THEREFOR COMPRISING THE COMBINATION: (A) A TUNNEL STRUCTURE; (B) MEANS FOR HEATING THE INTERIOR OF SAID TUNNEL STRUCTURE; (C) A FIRST SET OF SPACED CROSS-MEMBERS OF CERAMIC MATERIAL DISPOSED WITHIN SAID TUNNEL STRUCTURE TRANSVERSELY OF THE LINE OF CONVEYING MOVEMENT THERETHROUGH; (D) FIRST CARRIER MEMBERS EACH OF CERAMIC MATERIAL AND OF GENERALLY U-SHAPED SUPPORTED AT THEIR OPPOSITE ENDS ON ADJACENT CROSS-MEMBERS OF FIRST SET IN END-TOEND RELATIONSHIPS FOR DEFINING A FIRST GROUP OF SPACED LONGITUDINALLY-DISPOSED CARRIERS; (E) A SECOND SET OF SPACED CROSS-MEMBERS OF CERAMIC MATERIAL DISPOSED WITHIN SAID TUNNEL STRUCTURE TRANSVERSELY OF THE LINE OF CONVEYING MOVEMENT THERETHROUGH AND ARRANGED IN ALTERNATING DISPOSITION WITH RESPECT TO THE CROSS-MEMBERS OF SAID FIRST SET; 